UNCOVER: A NIRSpec Identification of a Broad-line AGN at z = 8.50

Kokorev, V ORCID: 0000-0002-5588-9156, Fujimoto, S ORCID: 0000-0001-7201-5066, Labbe, I ORCID: 0000-0002-2057-5376, Greene, JE ORCID: 0000-0002-5612-3427, Bezanson, R ORCID: 0000-0001-5063-8254, Dayal, P ORCID: 0000-0001-8460-1564, Nelson, EJ ORCID: 0000-0002-7524-374X, Atek, H ORCID: 0000-0002-7570-0824, Brammer, G ORCID: 0000-0003-2680-005X, Caputi, KI ORCID: 0000-0001-8183-1460, Chemerynska, I ORCID: 0009-0009-9795-6167, Cutler, SE ORCID: 0000-0002-7031-2865, Feldmann, R ORCID: 0000-0002-1109-1919, Fudamoto, Y ORCID: 0000-0001-7440-8832, Furtak, LJ ORCID: 0000-0001-6278-032X, Goulding, AD ORCID: 0000-0003-4700-663X, de Graaff, A ORCID: 0000-0002-2380-9801, Leja, J ORCID: 0000-0001-6755-1315, Marchesini, D ORCID: 0000-0001-9002-3502, Miller, TB ORCID: 0000-0001-8367-6265 et al (2023) UNCOVER: A NIRSpec Identification of a Broad-line AGN at z = 8.50. Astrophysical Journal Letters, 957 (1). ISSN 2041-8205

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Abstract

Deep observations with the James Webb Space Telescope (JWST) have revealed an emerging population of red pointlike sources that could provide a link between the postulated supermassive black hole seeds and observed quasars. In this work, we present a JWST/NIRSpec spectrum from the JWST Cycle 1 UNCOVER Treasury survey of a massive accreting black hole at z = 8.50 displaying a clear broad-line component as inferred from the Hβ line with FWHM = 3439 ± 413 km s−1, typical of the broad-line region of an active galactic nucleus (AGN). The AGN nature of this object is further supported by high ionization, as inferred from emission lines, and a point-source morphology. We compute a black hole mass of log 10 ( M BH / M ⊙ ) = 8.17 ± 0.42 and a bolometric luminosity of L bol ∼ 6.6 × 1045 erg s−1. These values imply that our object is accreting at ∼40% of the Eddington limit. Detailed modeling of the spectral energy distribution in the optical and near-infrared, together with constraints from ALMA, indicate an upper limit on the stellar mass of log 10 ( M * / M ⊙ ) < 8.7 , which would lead to an unprecedented ratio of black hole to host mass of at least ∼30%. This is orders of magnitude higher compared to the local QSOs but consistent with recent AGN studies at high redshift with JWST. This finding suggests that a nonnegligible fraction of supermassive black holes either started out from massive seeds and/or grew at a super-Eddington rate at high redshift. Given the predicted number densities of high-z faint AGN, future NIRSpec observations of larger samples will allow us to further investigate galaxy-black hole coevolution in the early Universe.

Item Type:	Article
Uncontrolled Keywords:	0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	American Astronomical Society
Date of acceptance:	15 October 2023
Date of first compliant Open Access:	11 December 2023
Date Deposited:	11 Dec 2023 16:29
Last Modified:	04 Jul 2025 15:15
DOI or ID number:	10.3847/2041-8213/ad037a
URI:	https://researchonline.ljmu.ac.uk/id/eprint/22080

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